This invention relates to temperature controlled radiation transmission materials and to their use for the reversibly temperature dependent control of the radiation transmission of buildings and of technical facilities.
The irradiation of closed spaces or technical apparatus, for example solar energy apparatus, with light causes them to heat tip to an extent which differs, and may even be harmful, with the energy content and the intensity of the light. For example, undesirable temperature values arise in buildings, greenhouses or cars because the energy content of sunlight varies with The time of day and season.
Prior artisans have therefore developed materials which are based on polymer blends which, as a function of the temperature, reversibly separate and thus become cloudy. The basis for the mechanism of this thermotropic behavior is that the structure of the polymer system changes at a certain temperature in such a way that its transmission of radiation changes. This phenomenon will usually arise when polymer blend components having different refractive indices separate at a certain temperature. The temperature at which this process takes place is known as the lower critical separation temperature (LCST). Fundamental explanations on the relationship between The structure of polymer blends and the occurrence of LCST behavior and on the use of polymer blends in glazing systems possessing temperature controlled light transmission may be found in EF-B-0 181 485.
Materials possessing improved reversibility of the change in radiation transmission are disclosed in EP-B-0 559 113 and DE-A 44 08 156.
EP-B-0 181 485 discloses plural component films comprising a polymeric mixture having a lower critical solution temperature (LCST), which are produced directly in one production stop by coextrusion, for example together with a base layer and/or a top layer. In the known plural component films the thermotropic polymer is disposed as a continuous layer between 2 layers composed of another polymer. The adhesion between the thermotropic polymer layer and base and/or top layers is therefore frequently insufficient and the coextruded films may delaminate in use.
It is an object of the present invention to provide plural component films which do not have the disadvantages of the prior art and which, more particularly, exhibit improved cohesion.
We have found that this object is achieved by a temperature controlled radiation transmission material for plural component films, the material being present in one or more cores allsidedly surrounded by a transparent sheath layer.
Temperature controlled radiation transmission polymer systems as described for example in DE-A 4 408 156, EP-B-0 181 485 or EP-B-0 559 113 tend to become sticky, especially at higher application temperatures, and their mechanical strength is low. We have determined that a transparent sheath layer which completely surrounds at least one core composed of one of the known thermotropic polymer blends provides stickiness control and mechanical strength and so makes it possible to put the thermotropic polymer blend into film form.
Moreover, the different refractive indices or core and sheath create the optical impression of a larger cote cross section (magnifying glass effect). The core comprises the costly special effect substance. By using the plural component film material of the invention it is thus possible to, obtain the same effect with a smaller amount or the costly special effect Substance as with a larger amount of unsheathed special effect substance.